1. Technical Field
The disclosure relates to a hybrid vehicle and, more particularly, to a control technique for suppressing deterioration of a secondary battery that is mounted on the hybrid vehicle.
2. Description of Related Art
Japanese Patent Application Publication No. 2013-125607 (JP 2013-125607 A) discloses a control device for a secondary battery that is mounted on a vehicle. This control device suppresses a high-rate deterioration of the secondary battery. According to JP 2013-125607 A, the high-rate deterioration is deterioration that is attributable to a salt concentration bias of the secondary battery resulting from charging and discharging continuously at a high rate. This control device calculates an evaluation value ΣD(N) that shows a degree of the high-rate deterioration of the secondary battery. This evaluation value ΣD(N) is defined in view of a progress of the high-rate deterioration attributable to charging entailed by an increase in secondary battery charging rate. In a case where the evaluation value ΣD(N) reaches a predetermined threshold that shows the deterioration attributable to excessive charging, the control device reduces an input electric power upper limit value (Win) that shows a limit value of the electric power with which the secondary battery is charged,
In this manner, the upper limit value of the charging electric power for the secondary battery is lowered by the control device in a case where the secondary battery undergoes the high-rate deterioration to some extent. As a result, the control device can suppress the deterioration of the secondary battery,
The inventors have found that a gradual salt concentration bias of the secondary battery occurs and the evaluation value ΣD(N) increases in a direction showing the excessive charging, even if the charging and discharging at a high rate do not continue to be performed, in a case where traveling is performed for a long period of time. In the following description, the “high-rate deterioration” will further include the deterioration of the secondary battery resulting from the salt concentration bias of the secondary battery occurring even if the charging and discharging at a high rate are not continuously performed.
In a case where the evaluation value ΣD(N) reaches the predetermined threshold that shows the deterioration attributable to excessive charging, the input electric power upper limit value is lowered, as in JP 2013-125607 A, so that the progress of the high-rate deterioration is suppressed. In this case, the amount of energy that can be recovered to the battery decreases, and thus fuel efficiency of the vehicle is worsened, In a case where the input electric power upper limit value is not lowered when the deterioration attributable to excessive charging occurs, the high-rate deterioration of the secondary battery is accelerated.
The progress of the high-rate deterioration of the secondary battery to the point of the evaluation value ΣD(N) reaching the predetermined threshold that shows the deterioration attributable to excessive charging might lead to a demerit in the form of the worsening of the fuel efficiency of the vehicle or the more rapid progress of the high-rate deterioration.